Molecular Dynamics Simulation of Interstitial He Diffusion on 〈110〉 Tilt Grain Boundaries in α-Iron

The migration of helium on different 〈110〉 high angle tilt grain boundaries (GBs) with misorientation angle varied from 26° to 140° in α-Fe was studied using atomistic simulations applying the recently developed Fe-He potentials. Systematic molecular static and molecular dynamics simulations were performed to calculate the binding energy between He and GBs, to estimate the diffusion coefficient and characterize migration mechanisms. The thermal stability of GBs was studied as well. The simulations were performed in the temperature range 300-1 200 K. The results show that all the GBs studied in this work are stable up to 1 200 K; both interstitial and substitutional helium are strongly bound to tilt GBs and the particular binding energy strongly correlates with the excess volume. The obtained results demonstrate that the migration mechanism and diffusivity of interstitial He are extremely sensitive to variations in atomic structure of the GBs.